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In basketball, players often have to take free throws - Leaving Cert Mathematics - Question 8 - 2015

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In basketball, players often have to take free throws. When Michael takes his first free throw in any game, the probability that he is successful is 0.7. For all sub... show full transcript

Worked Solution & Example Answer:In basketball, players often have to take free throws - Leaving Cert Mathematics - Question 8 - 2015

Step 1

Find the probability that Michael is successful (S) with all three of his first three free throws in a game.

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Answer

To determine this probability, we start by calculating the probability of success for each free throw. For the first throw, the probability of success is 0.7. For the second and third throws, since he was successful in the previous throw, the probability remains at 0.8 for both. Therefore, the calculation is as follows:

P(S,S,S)=0.7imes0.8imes0.8=0.448P(S, S, S) = 0.7 imes 0.8 imes 0.8 = 0.448

Step 2

Find the probability that Michael is unsuccessful (U) with his first two free throws and successful with the third.

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Here, we calculate the probability of being unsuccessful with the first two throws (which is 0.3 for each) and successful on the third throw (which is 0.8 when he is successful). Thus, we have:

P(U,U,S)=0.3imes0.3imes0.8=0.072P(U, U, S) = 0.3 imes 0.3 imes 0.8 = 0.072

Step 3

List all the ways that Michael could be successful with his third free throw in a game and hence find the probability that Michael is successful with his third free throw.

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The potential successful outcomes with the third throw can happen in the following ways:

  1. S, S, S
  2. S, U, S
  3. U, U, S
  4. U, S, S
  5. S, U, U

Therefore, we aggregate all paths that lead to a successful third throw:

P(S,S,S)+P(U,U,S)+P(S,U,S)+P(U,S,S)+P(S,U,U)=0.448+0.072+0.144+0.072+0.144=0.748P(S, S, S) + P(U, U, S) + P(S, U, S) + P(U, S, S) + P(S, U, U) = 0.448 + 0.072 + 0.144 + 0.072 + 0.144 = 0.748

Step 4

Show that $p_n = 0.6 + 0.2p_{n-1}$.

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To derive this, we consider:

pn=P(S,S)+P(U,S)p_n = P(S,S) + P(U,S)

Substituting in yields:

= 0.6 + 0.2p_{n-1}$$

Step 5

Using the result from part (d) (i) above, or otherwise, show that $p = 0.75$.

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By setting pnp_n^* to equal pp, we can replace this into the earlier equation:

p=0.6+0.2pp = 0.6 + 0.2p

This simplifies to

ightarrow p = 0.75$$

Step 6

Use the ratio $\frac{a_{n+1}}{a_n}$ to show that $a_n$ is a geometric sequence with common ratio $\frac{1}{5}$.

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Given that an=ppna_n = p - p_n, the ratio is computed as follows:

an+1an=ppn+1ppn=0.75pn+10.75pn=0.150.2pn0.15=15\frac{a_{n+1}}{a_n} = \frac{p - p_{n+1}}{p - p_n} = \frac{0.75 - p_{n+1}}{0.75 - p_n} = \frac{0.15 - 0.2p_{n}}{0.15} = \frac{1}{5}

Step 7

Find the smallest value of n for which p - p_n < 0.00001.

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We know that:

a_n = 0.05\(0.5)^{n-1} < 0.00001$$ This gives us a logarithmic equation: $$(n - 1) \cdot \ln(0.5) < \ln(0.00001)$$ Solving yields: $$n > 6.29 \rightarrow n = 7$$

Step 8

What is your estimate of the probability that Michael will be successful with his next free throw?

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Answer

Based on the previous calculations, the estimated probability is pp, which evaluates to 0.75.

Step 9

Why would it not be appropriate to consider Michael's subsequent free throws in the game as a sequence of Bernoulli trials?

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Answer

Michael's throws are not independent events. The outcome of each throw affects the probability of succeeding on the subsequent throw.

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